Rebel fighters take part in a demonstration against the Syrian regime after Friday prayers. / Odd Andersen AFP, Getty Images

by Mona Alami, Special for USA TODAY

by Mona Alami, Special for USA TODAY

BEIRUT - Syrian rebels said Friday that they were close to surrounding an international airport outside the capital that the regime of dictator Bashar Assad has been using as a base to ferry troops and bomb rebellious cities.

Damascus International Airport is about 15 miles east of the heart of the city and government troops have been battling for days to keep it out of the hands of rebel forces. Clashes between government troops and rebels forced the closure of the airport road for the second time this week.

The rebels have survived punishing airstrikes for months in several cities throughout an uprising that has killed an estimated 40,000 people since it began in March 2011. The attack on the airport is the closet the rebels have gotten to the heart of the regime in Damascus.

Brigades for the Free Syrian Army, the outfit of deserters and others who have led the rebellion, said they were about a half-mile from the airport and holding their positions despite massive artillery fire from Syrian troops.

"The FSA has practically encircled the airport," Free Syrian Army spokesman Musab Abu Qatada said in a telephone interview.

Abu Qatada said the FSA has received information that most planes from the Damascus airport had been moved north to the city of Lattaquieh and that commercial flights were grounded. He said the rebels hope to take the airport soon.

"When it happens, the regime would lose its connection with the outside world," he said. "This would mean a significant military defeat."

His claims could not be independently verified. The clashes did force the suspension of commercial flights over the past week but an airport official said Friday the facility was still functioning. The official declined to be identified because he was not authorized to give official statements.

Syrian activist Mourad al Chami said more than 100 people had been killed in clashes this week in Syria, including in suburbs of Damascus and Deir al Zour in eastern Syria. He said clashes had erupted inside Damascus in the vicinity of the Yarmouk Palestinian camp.

Abu Qatada said some rebels were worried that the regime may resort to using chemical weapons to survive and that he has heard reports that Syrian troops had received gas masks.

He said phosphorus bombs have already been used on Daraya a few miles south of Damascus, "causing cases of asphyxia among the population."

Assad's foreign ministry has said it would not use chemical weapons and Assad has said he would continue to fight a rebellion he says is made up of terrorists backed by Western governments.

Rebels said taking the airport would cut into onto the military's resupplying chain. Iran and Russia have been accused by the United States of supplying Syria with weapons through the airport.

Also on Friday, U.N. Secretary-General Ban Ki Moon renewed a call for Syria to not use chemical weapons, saying the move would amount to an "outrageous crime" against humanity. George Sabra, head of the Syrian National Council opposition group, called on Syrian soldiers to ignore any orders to use them.

"Any civilian or military Syrian, who implements or helps implement this crime will be held accountable as a traitor for this country and will be pursued on charges of committing genocide," he said at a news conference in Paris.

"The Syrian people will not forgive or have mercy on anyone who orders the use of weapons of destruction and anyone who participates in executing this crime," he added.